This application is a continuation of PCT/JP00/06627, filed Sep. 26, 2000. This application is also related to and claims priority to JP 11/281920, filed Oct. 1, 1999.
1. Field of the Invention
The present invention relates to novel aspartyl dipeptide ester derivatives that are safe, have a taste similar to that of sugar and a high degree of sweetness, for instance, to compounds which are at least 10,000-times sweeter than sugar. The invention also encompasses sweeteners comprising these aspartyl dipeptide ester derivatives, as well as products, such as foods and drinks, containing such sweeteners. Methods for making and using the sweeteners of the present invention are also described.
2. Description of the Related Art
In recent years, the development of low-calorie sweeteners has been demanded due to changes in eating habits, such as increased fatness caused by excessive intake of sugar, as well as due to the prevalence of various diseases associated with fatness.
Aspartame is a sweetener that is presently widely used and is excellent in terms of safety and for its sweetening qualities. However, the stability of aspartame is problematic.
Slight improvements in stability as well as improvements in sweetening potency have been reported for aspartame derivatives obtained by introducing an alkyl group into a nitrogen atom of aspartic acid in aspartame, see Kokai Publication of the International Patent WO 94/11391. Most excellent among compounds described in this Publication is N-[N-(3,3-dimethylbutyl)-L-xcex1-aspartyl]-L-phenylalanine 1-methyl ester having a 3,3-dimethylbutyl group as an alkyl group, and the sweetening potency (degree of sweetness) is 10,000 times that of sucrose (compared with 2, 5 and 10% sucrose solutions).
Other aspartame derivatives having introduced therein 20 types of substituents other than the 3,3-dimethylbutyl group are also described. However, the sweetening potencies (degrees of sweetness) of all these derivatives has been reported to be not more than 2,500 times.
Derivatives having a 3-(substituted phenyl)propyl group as an alkyl group are also described. With respect to derivatives having a relatively high sweetening potency among them, it is reported that a sweetening potency of N-[N-(3-phenylpropyl)-L-xcex1-aspartyl]-L-phenylalanine 1-methyl ester is 1,500 times and a sweetening potency of N-[N-[3-(3-methoxy-4-hydroxyphenyl)propyl]-L-xcex1-aspartyl]-L-phenylalanine 1-methyl ester is 2,500 times. However, the sweetening potencies of these derivatives do not reach the potency (10,000 times that of sugar) of N-[N-(3,3-dimethylbutyl)-L-xcex1-aspartyl]-L-phenylalanine 1-methyl ester.
Further, it is reported that the sweetening potency of N-[N-[(RS)-3-phenylbutyl]-L-xcex1-aspartyl]-L-phenylalanine 1-methyl ester having a substituent of a structure that a methyl group is further introduced in the 3-position of a 3-phenylpropyl group, namely a 3-phenylbutyl group as an alkyl group is only 1,200 times. Thus, by introducing the methyl group in the 3-position, the sweetening potency is decreased in comparison with N-[N-(3-phenylpropyl)-L-xcex1-aspartyl]-L-phenylalanine 1-methyl ester.
Thus, the development of sweeteners that solve the aforementioned problems and which are safe, taste like sugar, have greater stability, and/or have a much higher sweetening potency has been in demand.
The present invention solves the problems of prior art sweeteners mentioned above, such as low sweetening potency, by providing a novel aspartyl dipeptide ester derivative excellent in safety, having a sweet taste similar to sugar and a sweetening potency which is equal to or higher than that of the N-[N-(3,3-dimethylbutyl)-L-xcex1-aspartyl-L-phenylalanine 1-methyl ester described above. The invention also encompasses sweeteners, such as low-calorie sweeteners, and foods and drinks containing these more potent sweeteners.
To solve the foregoing problems, the present inventors have synthesized various compounds in which various 3-(substituted phenyl)propyl groups, for example, a 3,3-dialkyl-3-(substituted phenyl)propyl group, are introduced into nitrogen of aspartic acid constituting aspartame by a reductive alkylation reaction using 3-phenylpropionaldehyde derivatives or cinnamaldehyde derivatives (including derivatives having an alkyl substituent in a main chain) having various substituents, especially two or more hydroxyl groups in a phenyl group, and have examined a sweetening potency thereof.
As a result, compounds have been discovered that have a sweetening potency which is by far higher than that of N-[N-(3,3-dimethylbutyl)-L-xcex1-aspartyl]-L-phenylalanine 1-methyl ester, which has been reported to have a sweetening potency of 10,000 times in the foregoing Kokai Publication of the International Patent WO 94/11391, not to mention N-[N-[(RS)-3-phenylbutyl]-L-xcex1-aspartyl]-L-phenylalanine 1-methyl ester reported therein to have a sweetening potency of 1,200 times, N-[N-3-(3-methoxy-4-hydroxyphenyl)propyl]-L-xcex1-aspartyl]-L-phenylalanine 1-methyl ester reported therein to have a sweetening potency of 2,500 times, and the like.
In particular it has been found that compounds represented by the following general formula (1) are especially excellent as sweeteners and the present invention has been completed on the basis of this finding. That is, the present invention lies in aspartyl dipeptide ester derivatives represented by the following general formula (1) (including those in the form of salts), sweeteners and products, such as foods and drinks, and the like comprising the same, and in a method for imparting sweetness to various products.
Formula (1) 
wherein R1, R2, R3, R4 and R5 independently from each other, represent a hydrogen atom (H) or a hydroxyl group (OH), at least any two selected from R1, R2, R3, R4 and R5 are hydroxyl groups, and R6 and R7, independently from each other, represent a hydrogen atom (H) or an alkyl group having 1 to 3 carbon atoms (CH3, CH2CH3, CH(CH3)2 or the like).
When R6 and R7 represent different substituents, a steric configuration of a carbon atom to which these substituents are bound is not particularly limited, and it may be any of (R), (S) and (RS), or a mixed form of these plural forms. Incidentally, in the general formula (1) described above, the binding site (linkage) between R6 or R7 and the carbon atom is indicated by a wavy line, meaning that there are no limitations on the direction of linkage.
The compounds represented by the general formula (1) described above and those in the form of salts are both included in the novel aspartyl dipeptide ester derivatives of the present invention.
When they are incorporated in sweeteners and the like, it is advisable that at least one compound or at least one compound in the form of a salt is incorporated. Accordingly, one of the compounds or a mixture of more than one thereof, one of the salts of the compounds or a mixture of more than one thereof, a mixture of the compound(s) and the salt(s) of the compound(s), and the like can all be incorporated in sweetener(s), foods and drinks and the like of the present invention.
Amino acids (aspartic acid and phenylalanine) constituting the derivatives described above are both preferably L-isomers because they are present in nature.
With respect to the preferable forms of the compounds, the following inventions are included in the compounds of the present invention.
[1] Compounds represented by the general formula (1) described above.
In the general formula (1), R1, R2, R3, R4 and R5, independently from each other, represent a hydrogen atom (H) or a hydroxyl group (OH), and at least any two selected from R1, R2, R3, R4 and R5 are hydroxyl groups, and
R6 and R7, independently from each other, represent a hydrogen atom (H) or an alkyl group having 1 to 3 carbon atoms (CH3, CH2CH3, CH(CH3)2 or the like).
When R6 and R7 represent different substituents, a steric configuration of a carbon atom to which these substituents are bound is not particularly limited, and it may be any of (R), (S) and (RS).
[2] Compounds described in (1) above in which in the formula any two selected from R1, R2, R3, R4 and R5 are hydroxyl groups.
[3] Compounds described in (1) above in which in the formula any three selected from R1, R2, R3, R4 and R5 are hydroxyl groups.
[4] Compounds described in (1) above in which in the formula R6 and R7 are hydrogen atoms.
[5] Compounds described in (1) above in which in the formula R6 is a methyl group.
[6] Compounds described in (1) above in which in the formula R7 is a methyl group.
[7] Compounds described in (1) above in which in the formula R1 and R3 are hydroxyl groups, and R2, R4, R5, R6 and R7 are hydrogen atoms.
[8] Compounds described in (1) above in which in the formula R2 and R3 are hydroxyl groups, and R1, R4, R5, R6 and R7 are hydrogen atoms.
[9] Compounds described in (1) above in which in the formula R1, R2 and R3 are hydroxyl groups, and R4, R5, R6 and R7 are hydrogen atoms.
[10] Compounds described in (1) above in which in the formula R2, R3 and R4 are hydroxyl groups, and R1, R5, R6 and R7 are hydrogen atoms.
[11] Compounds described in (1) above in which in the formula R2 and R3 are hydroxyl groups, R1, R4 and R5 are hydrogen atoms, and R6 and R7 are methyl groups.
[12] Compounds described in (1) above in which when R6 and R7 in the formula represent different substituents, the steric configuration of the carbon atom to which R6 is bound is any of (R), (S) and (RS).
The present invention also includes the following inventions as preferable embodiments.
[13] Sweeteners, foods and drinks having a sweetness and other products having a sweetness, comprising the derivatives (including those in the form of salts) of the present invention as an active ingredient.
Further, a carrier and/or a filler (a bulking agent) for sweeteners may be contained therein. As described above, at least one of the derivatives described above can be contained in the sweeteners and the like described above.
[14] A method for imparting a sweetness (a sweet taste) wherein the derivative(s) of the present invention is contained (mixed or added) in products requiring a sweetness (foods and drinks, pharmaceuticals, oral sanitary products and the like) and intermediate products during the production stage thereof.
The method for using the derivatives of the present invention in the production stage of sweeteners, products and the like is not particularly limited, and it can be conducted using a method known as a method for using sweet ingredient(s) or various methods which will be developed in future.
The derivatives of the present invention include the compounds represented by the formula (1) or salts thereof. Examples of the salts of the compounds include salts with alkali metals such as sodium, potassium and the like, salts with alkaline earth metals such as calcium, magnesium and the like, ammonium salt with ammonia, salts with amino acids such as lysine, arginine and the like, salts with inorganic acids such as hydrochloric acid, sulfuric acid and the like, salts with organic acids such as citric acid, acetic acid and the like, and salts with other sweeteners such as saccharin, acesulfame, cyclamic acid, glycyrrhizic acid and the like. These are also included in the derivatives of the present invention as stated above.
It is not particularly difficult to produce the aspartyl dipeptide ester derivatives of the present invention. Preferably, they can easily be formed by reductively alkylating aspartame with 3-phenylpropionaldehyde derivatives or cinnamaldehyde derivatives (including derivatives having alkyl substituent(s) in a main chain) having various substituents in a phenyl group and a reducing agent (for example, hydrogen/palladium carbon catalyst). Alternatively, they can be formed by a method which comprises reductively alkylating aspartame derivatives (for example, xcex2-O-benzyl-L-xcex1-aspartyl-L-phenylalanine methyl ester) having a protecting group in a carboxyl group in the xcex2-position which can be obtained according to an ordinary peptide synthesis method (refer to Izumiya et al., pepuchido gosei no kiso to jikken [Base and Experiment of Peptide Synthesis]: Maruzen, published Jan. 20, 1985) with the foregoing 3-phenylpropionaldehyde derivatives or cinnamaldehyde derivatives and a reducing agent (for example, NaB(OAc)3H) (refer to A. F. Abdel-Magid et al., Tetrahedron Letters, 31, 5595 (1990)) and thereafter removing the protecting group therefrom, or a method in which an unsaturated bond is saturated with a reducing agent as required. However, the process for producing the compounds of the present invention is not limited thereto. Of course, their acetals or the like can be used as an aldehyde component in the reductive alkylation instead of the foregoing 3-phenylpropionaldehyde derivatives or cinnamaldehyde derivatives.
As a result of an organoleptic (sensory) test, it was found that the derivatives of the present invention, namely, the compounds and those in the form of salts in the present invention had a quality of sweet taste similar to that of sugar and a strong sweetness. For example, a sweetening potency of N-[N-[3-(3,4-dihydroxyphenyl)-3-methylbutyl]-L-xcex1-aspartyl]-L-phenylalanine 1-methyl ester was approximately 50,000 times (relative to sugar), and a sweetening potency of N-[N-[3-(3,4,5-trihydroxyphenyl)propyl]-L-xcex1-aspartyl]-L-phenylalanine 1-methyl ester was approximately 25,000 times (relative to sugar).
The structures and the results of the sensory test on some aspartyl dipeptide ester derivatives (represented by the following general formula (1)) formed are shown in Table 1.
As is clear from the results in Table 1, it is understood that the novel derivatives of the present invention are especially excellent in the sweetening potency. 
Incidentally, when the derivatives of the present invention (including the compounds of the present invention and those in the form of salts) are used as sweeteners, they may naturally be used in combination with other sweeteners unless inviting particular or special troubles.
When the derivatives of the present invention are used as sweeteners, a carrier and/or a filler (bulking agent) may be used as required. For example, a carrier, a filler and the like for sweeteners which have been so far known or used are available.
The derivatives of the present invention can be used as sweeteners or sweetener ingredients, and further as sweetness-imparting ingredients of various products such as food and drink and the like required to have a sweetness (sweet taste), for example, confectionery, chewing gum, sanitary (hygiene) products, toiletries (cosmetics), pharmaceuticals, products for animals except humans, and so forth. The derivatives of the present invention can also be used in the form of sweetened products or in methods for imparting sweetness to products required to have sweetness. Conventional methods for sweetening products may be used.